ABSTRACT
The complexes (Bu4N)(LMeM(II)-OH) (LMe = 2,6-dimethylphenyl-substituted pyridine(dicarboxamide); M = Cu or Ni) react with CH3CN to yield (Bu4N)(LMeM-CH2CN), novel cyanomethide complexes that were fully characterized, including by X-ray crystallography. These conversions contrast with the usual reactions of metal-hydroxide complexes with nitriles, which typically involve attack at the nitrile carbon and formation of amides or carboxylic acids. Kinetic studies (M = Cu) revealed a first-order dependence on the complex and a kinetic isotope effect (k(CH3CN)/k(CD3CN) of 4. Various mechanisms involving either intra- or intermolecular deprotonation steps are proposed. In addition, (Bu4N)(LMeCu-OH) was oxidized by Fc+PF6- to a proposed Cu(III) complex LMeCuOH at low temperature, and comparisons of its stability and reactivity with dihydroanthracene were drawn to its previously described congener having isopropyl substituents on the phenyl rings of the supporting ligand. The cyanomethide complex (Bu4N)(LMeCu(CH2CN)) also was reversibly oxidized both electrochemically (E1/2 = -0.345 V vs. Fc/Fc+) and chemically (Fc+PF6-, -25 °C). The product was formulated as LMeCu(III)(CH2CN), a novel Cu(III)-alkyl complex relevant to such species proposed during copper-catalyzed organic reactions.
ABSTRACT
One-electron oxidation of the tetragonal Cu(II) complex [Bu(4)N][LCuOH] at -80 °C generated the reactive intermediate LCuOH, which was shown to be a Cu(III) complex on the basis of spectroscopy and theory (L = N,N'-bis(2,6-diisopropylphenyl)-2,6-pyridinedicarboxamide). The complex LCuOH reacts with dihydroanthracene to yield anthracene and the Cu(II) complex LCu(OH(2)). Kinetic studies showed that the reaction occurs via H-atom abstraction via a second-order rate law at high rates (cf. k = 1.1(1) M(-1) s(-1) at -80 °C, ΔH() = 5.4(2) kcal mol(-1), ΔS() = -30(2) eu) and with very large kinetic isotope effects (cf. k(H)/k(D) = 44 at -70 °C). The findings suggest that a Cu(III)-OH moiety is a viable reactant in oxidation catalysis.
Subject(s)
Copper/chemistry , Hydroxides/chemistry , Organometallic Compounds/chemistry , Crystallography, X-Ray , Models, Molecular , Molecular StructureABSTRACT
In the exploration of sulfur-delivery reagents useful for synthesizing models of the tetracopper-sulfide cluster of nitrous oxide reductase, reactions of Ph(3)SbâS with Cu(I) complexes of N,N,N',N'-tetramethyl-2R,3R-cyclohexanediamine (TMCHD) and 1,4,7-trialkyltriazacyclononanes (R(3)tacn; R = Me, Et, iPr) were studied. Treatment of [(R(3)tacn)Cu(NCCH(3))]SbF(6) (R = Me, Et, or iPr) with 1 equiv of SâSbPh(3) in CH(2)Cl(2) yielded adducts [(R(3)tacn)Cu(SâSbPh(3))]SbF(6) (1-3), which were fully characterized, including by X-ray crystallography. The adducts slowly decayed to [(R(3)tacn)(2)Cu(2)(µ-η(2):η(2)-S(2))](2+) species (4-6) and SbPh(3), or more quickly in the presence of additional [(R(3)tacn)Cu(NCCH(3))]SbF(6) to 4-6 and [(R(3)tacn)Cu(SbPh(3))]SbF(6) (7-9). The results of mechanistic studies of the latter process were consistent with rapid intermolecular exchange of SâSbPh(3) between 1-3 and added [(R(3)tacn)Cu(NCCH(3))]SbF(6), followed by conversion to product via a dicopper intermediate formed in a rapid pre-equilibrium step. Key evidence supporting this step came from the observation of saturation behavior in a plot of the initial rate of loss of 1 versus the initial concentration of [(Me(3)tacn)Cu(NCCH(3))]SbF(6). Also, treatment of [(TMCHD)Cu(CH(3)CN)]PF(6) with SâSbPh(3) led to the known tricopper cluster [(TMCHD)(3)Cu(3)(µ(3)-S)(2)](PF(6))(3) in good yield (79%), a synthetic procedure superior to that previously reported (Brown, E. C.; York, J. T.; Antholine, W. E.; Ruiz, E.; Alvarez, S.; Tolman, W. B. J. Am. Chem. Soc. 2005, 127, 13752-13753).
Subject(s)
Antimony/chemistry , Copper/chemistry , Organometallic Compounds/chemical synthesis , Sulfides/chemistry , Crystallography, X-Ray , Ligands , Models, Molecular , Molecular Structure , Organometallic Compounds/chemistry , StereoisomerismABSTRACT
Recent broad-ranging mechanistic studies of FeIII-TAML peroxide activators enable a strategy for designing catalysts with improved (i) hydrolytic and (ii) operational stabilities, (iii) faster activation of H2O2 and other peroxides, and (iv) a pH of highest activity closer to 7. Combining all items of insight leads to [Fe{1-NO2C6H3-3,4-(NCOCMe2NCO)2CF2}(OH2)]- (1a) which exhibits the most desirable technical performance in its class.
